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What have twin studies shown about genetic and environmental influences on autism spectrum disorder?

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autism American artist Chris Murray, who has autism, at work.

Research involving twin studies has provided significant insights into the origins of autism spectrum disorder (ASD). While the exact causes of autism remain unclear, these studies indicate that both genetic and environmental factors contribute to its development.12

A notable study published in 2011, which assessed pairs of twins where at least one individual was affected by an ASD, suggested that while genetic factors contribute moderately to susceptibility, environmental factors appear to contribute to a greater degree.1

The twin method is a standard tool in behaviour genetics used to screen for these influences. By comparing identical (monozygotic) twins, who share all their genes, with fraternal (dizygotic) twins, who share only about half, researchers can estimate the relative impact of heredity versus environment. Current scientific understanding emphasizes that interactions between genes and the environment play a critical role in influencing the condition.31